This is a adaptation of my inventions disclosed in U.S. Pat. Nos. 5,070,063, issued Dec. 10, 1991 and 5,199,159, issued Apr. 6, 1993. My prior U.S. Pat. No. 5,070,063 related generally to a method of separating printed circuit wiring boards and, more particularly, to a method of cyrogenically separating multi-layer printed circuit wiring boards without damaging the printed circuit on the individual layers. My prior U.S. Pat. No. 5,199,159 involved the cryogenic removal of the field windings of a generator or motor. This invention involves the method of removing focusing coils from their rigid housings without damaging the housings.
Focusing coils are comprised of an assembly including an inner lead liner, an epoxy encapsulated coil, and an outer brass housing. During manufacture, the epoxy on the coil bonds the coil to both the liner and the housing. If the coil becomes defective, it is desirable to re-use the liner and housing, since these are expensive items to replace. In the past, the outer brass housing with the focusing coil in place, and containing the inner lead liner along with a brass rear flange were placed in a burn out furnace. The furnace was then heated to 500.degree. F. for 20 hours. This was done in a reducing environment (without oxygen). The toxic gases and the ash resulting from this burn out were released into the environment via the foundry chimney. In some cases, the epoxy was not completely ashed, and the apparatus was put through a second heating cycle. The coil was then removed from the outer housing by hand. The personnel were required to wear a respirator, gloves, coveralls, and other protective gear. The whole operation was labor intensive, and in some cases the lead shield melted so that additional precautions had to be taken to protect the personnel. In addition, the venting of the ash and gases up the foundry stack created an environmental hazard.